Pozzolanic cements

Certain treatment systems fall in the category of cement-pozzolanic processes and have been in use for some time outside the U.S. In these systems, both cement and lime-siliceous materials are used in combination to give the best and most economical containment for the specific waste being treated In general, the bulk of the comments (under both classifications above) hold for techniques using a combination of treatment materials. 

SOLFIX is an ex situ stabilization technology that treats heavy metals by reacting contaminated soils and sediments with cement, pozzolanic materials, and other additives to chemically immobilize contaminants into an insoluble form. SOLFIX can be used either as a stand-alone technology or it can be incorporated with Hydro-SEP (a sediment washing technology) and ORG-X (a solvent extraction technology) into a three-step remediation process termed integrated sediment decontamination system (ISDS). 

Some important nonmetallic inorganic materials used in construction are cements pozzolanic materials and slags clays calcium sulfates and rocks, aggregates, sand, and glass. 

In hardened cement-based composites the transportation of liquids and gases through pore and microcrack systems plays a very important role in many processes, such as hydration of Portland cement, pozzolane effects of microfillers, carbonation, corrosion of cement paste and reinforcement due to reaction with external agents, shrinkage and creep, etc. These processes are partly described in respective Sections 4.1, 4.3, 6.5 and 11.5. Only basic information is reiterated below concerning the flow of liquids and gases through concretes and mortars. 

Add the cementitious materials (cement + pozzolans) slowly with another one-third of the mixing liquids to preserve fluidity and workability of the mixture. 

Petroleum. Apart from its use ia petrochemicals manufacture, there are a number of small, scattered uses of lime ia petroleum (qv) production. These are ia making red lime (drilling) muds, calcium-based lubricating grease, neutralization of organic sulfur compounds and waste acid effluents, water treatment ia water flooding (secondary oil recovery), and use of lime and pozzolans for cementing very deep oil wells. 

Some of the most common stabilization—soHdification processes are those using cement, lime, and pozzolanic materials. These materials are popular because they are very effective, plentiful, and relatively inexpensive. Other stabilization—soHdification technologies include thermoplastics, thermosetting reactive polymers, polymerization, and vitrification. Vitrification is discussed in the thermal treatment section of this article and the other stabdization—soHdification processes are discussed below. 

Major categories of industrial waste solidiflcation/stabilization systems are cement-based processes, pozzolanic processes (not including cement), thermoplastic techniques, organic polymer techniques, surface encapsulation techniques, and self-cementing techniques (for high calcium sulfate sludges). Vitrification (discussed previously) can also be considered a solidification process. 

Adding large quantities of pozzolan, ceramic microspheres or nitrogen. These materials lighten the slurry because they have lower specific gravities than the cement. 

The most common low-specific-gravity solids used to reduce cement slurry specific weight are bentonite, diatomaceous earth, solid hydrocarbons, expanded perlite and pozzolan. It may not be possible to reduce the cement slurry specific weight enough with the above low-specific-weight materials when very weak formations are exposed. In such cases nitrogen is used to aerate the mud column above the cement slurry to assist in further decreasing the hydrostatic pressure. 

Pozzolan. Diatomaceous earth is a type of pozzolan. Pozzolan refers to a finely ground pumice or fly ash that is marketed as a cement additive under that name. The specific gravity of pozzolans is slightly less than the specific gravity of cement. The water requirements for this additive are about the same as for cements. Only a slight reduction in specific weight of a slurry can be realized by using these additives. The cost of pozzolans is very low. 

Petrifix A process for solidifying aqueous wastes, converting them to a solid form suitable for landfill. Cementitious additives are used, based on the compositions used by the Romans for making Pozzolanic cements. Developed by Pec-Engineering, Paris, France. In 1979 it had been used in France and Germany. 

Solidification of the upper layers can be accomplished by blending pozzolanic additives, modified clay, or stabilization reagents into moist soil and compacting the mass. Pozzolanic additives include such fixatives as portland cement, quick lime,... 

Mordenite and cHnoptiloHte are used in small volume in adsorbent applications including air separation and in drying and purification [24]. Natural zeolites have also found use in bulk applications as fillers in paper, in pozzolanic cements and concrete, in fertihzer and soil conditioners and as dietary supplements in animal husbandry. 

Methods of preventing alkali-aggregate expansion reactions in concrete consist of avoidance of reactive aggregates, use of cement with alkalis less than 0.6% Na20 equivalent, the use of pozzolanic materials, sealing of... 

The HAZCON solidification process is an ex situ technology for the immobilization of metals and inorganic hazardous wastes in wet or dry soil and sludges. The technology is a cement-based process in which the contaminated material is mixed with pozzolanic materials such as Portland cement, a patented additive called Chloranan, and water. The process is capable of treating solids, sludges, semisolids, or liquids. The mixture hardens into a cohesive mass that immobilizes heavy metals. 

Pozzolanic S/S systems use portland cement and pozzolan materials (e.g., fly ash) to produce a strucmrally stronger waste/concrete composite. The waste is contained in the concrete matrix by microencapsulation (physical entrapment). It is a chemical treatment that uses commercially available soluble silicate solutions and various cementious materials such as cement, lime, poz-zolans, and fly ash. By addition of these reagents and rigorous mixing, the waste is fixed or stabilized. Contaminant mobility is reduced through the binding of contaminants within a solid matrix, which reduces permeability and the amount of surface area available for the release of toxic components. 

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